1. Field of the Invention
This invention relates generally to electric generators and more particularly to electric generators which are powered by the rotation of a wheel assembly.
2. Description of the Prior Art
It is often desirable to have a source of electrical power located at the wheel of a car. For example, monitoring devices could be provided at the wheel to detect when the tire pressure is low, or the wheel temperature is too high. Also, visual safety devices such as wheel lights could be provided to make the car more visible under night driving conditions.
Batteries are an inexpensive and convenient power source, but suffer from the disadvantage that they will, with time, become discharged and inoperable. Because of this problem a number of devices have been developed which attach a generator to the outside of the wheel to provide small amounts of electric power.
For example, in U.S. Pat. No. 4,229,728 of Tremba, a hubcap generator is disclosed including a permanent magnetic attached to a weighted pendulum which is supported by a centrally located pin. A pickup coil is wrapped around a core such that as the wheel is rotated, the core rotates with it and the permanent magnet remains stationary.
A problem with wheel mounted generators of the prior art is that the amount of power produced by such devices is small. The power provided may be sufficient for sensing circuits which draw relatively little power, but tend to be inadequate for high power applications such as illuminating safety lights attached to the wheel.
Another problem with the prior art generators is that their output at slow speeds is so small that the sensing circuits that they power may become inoperable. Furthermore, the power output to weight ratio of prior art generators is very poor.